When a catheter or other medical device is used in a body cavity, such as an artery, the mechanical rubbing of the catheter, or inflation of the balloon of a balloon angioplasty catheter, or the placement of a stent, can trigger the body to react to such mechanical injury. The body reacts by, among other processes, producing smooth muscle cell and fibroblast migration to the injury site. The body, depending on the location, may also produce endothelial cells and epithelial cells at injury site.
In the case of balloon angioplasty, such reaction by the body will cause a build-up of scar tissue, which can eventually negate the process of angioplasty that was performed in the first place. In other instances, stents are placed in blood vessels to keep the lumen open after angioplasty. The presence of stents, a foreign body, also triggers a set of events for the body to produce smooth muscle cells and causes fibroblast migration to cover-up the struts of the stent, which eventually closes the lumen to a greater or lesser degree.
In addition to the migration of cells, (smooth muscle cells and fibroblasts) another phenomenon that causes closure of vessels after intervention is spasm. Spasm also contributes, more acutely, to the vessel closure resulting, in some instances, to grave consequences.
Many methods have been tried to prevent this process of cell proliferation/migration. In addition to mechanical methods such as stents, various, chemical and combination treatments have been tried.
In the area of drug treatment of the injury site, several inventors have proposed different methods and drugs. Muller, U.S. Pat. No. 5,947,928 suggests a shock wave mechanism to transfer the drug to the needed location. Also, drugs have been embedded or coated in stents for delivery into the vessel wall. Recent results of drug-coated stents have shown some serious draw backs. These include inflammation of the tissue and the presence of “black holes” in the area covered by the stent. Although the exact reason for the black holes is not yet understood, the absence of such black holes in un-coated stents points to the fact the black holes are due to the drug and the coating. Such “black holes” are vacuous areas between the outer surface of the stent and the vessel wall which allow cellular elements to begin to collect there, eventually producing obstruction extending into a lumen of the stent. Although the exact reason for the black holes is not yet understood, the absence of such black holes in un-coated stents points to the fact the black holes are due to the drug and the coating.
Among other treatment methods, laser light has been used in several ways to address the problem. Laser and light treatment has been used in medicine widely both on the skin and outer tissues of the body and inside the body cavity in blood vessels, trachea, lungs and in the gastrointestinal track. The advantage of light and laser is the ability to control the wavelength and the power so that the tissue can absorb the energy at the desired level.
For example, Daikuzono, et. al, U.S. Pat. No. 6,024,738 describes a flexible conduit positioned by a balloon for carrying laser energy for ablating and melting the plaque in arteries.
Pruitt Sr., U.S. Pat. No. 5,993,382 describes a lighted catheter device and an optical fiber delivering light to the desired location by positioning the end of the light fiber between two balloons. Pruitt's main purpose is to illuminate the location of the lesion, and he describes a method to deliver the light energy to the desired location isolated by two occluding balloons. Other methods of delivering laser light, have been described by Ishibashi, U.S. Pat. No. 4,567,882 employing a prism or a bifurcated emitter portion, Ector, U.S. Pat. No. 4,567,882 employing a hemispherical tip formed on the end of the fiber/catheter tip, Mackin, U.S. Pat. No. 4,961,738 using diverging optical fibers, Sugiyama, et al, U.S. Pat. No. 5,036,834 who employed Lens and Kozawa, U.S. Pat. No. 5,335,648 using a mirror to reflect the light energy. Hillsman, U.S. Pat. No. 5,643,251 described a method and apparatus for ablating an obstruction. As is now known in the medical field, laser light ablation produces severe scar tissue and actually compounds the injury caused by mechanical means such as balloons or stents.
Littleford, et. al., U.S. Pat. No. 4,834,073 describes a combination of laser ablation and angioplasty process. Lennox, et. al., U.S. Pat. No. 5,454,807 also describes a method and apparatus, using a light guide, to deliver light and a cooling medium for light irritation.
Most inventors have used light energy in the form of laser and as light to ablate or melt the obstruction or treat the area in way of energy that eventually transforms into energy absorbed by the tissue as heat.
Several complex methods have been adopted to bend the laser light or light using lenses, mirrors etc. so that the treatment area receives the laser light. Various occlusion devices have been used to either centrally locate the laser beam or as means of getting rid of blood and other fluids from the area of treatment. Many have attempted to use a cooling fluid to cool the area of treatment to avoid thermal injury.
All these methods are complex in nature and quite difficult to practice. Occlusion devices stop the blood flow to the organ thereby producing ischemic manifestations in the organ.
Another major vascular disease that affects a large number of patients is vulnerable plaque. Vulnerable plaque can be described as atherosclerotic plaque containing a lipid pool, which is covered by a thin fibrous capsule over a layer of collagen and elastin that gives tensile strength to this exracellular matrix. The fibrous capsule typically is a single layer of endothelial cells, which may be eroded by both inflamatatory T-Lymphocytes and invading smooth muscle cells. Activated macrophages moving into the plaque from the vasa vasorum produce protelytic enzymes that promote collagen degradation causing cap disruption and thrombogenic surface activation associated with acute coronary syndromes. The capsule is quite unstable and when ruptured due to various causes release the lipids to the blood stream, which causes clotting. The clots so formed can be instrumental in causing a myocardial infarction or heart attack when the arteries involved are the coronary arteries.
Several inventors have developed means to identify and diagnose the existence of vulnerable plaque. Moreno et. al. in Patent Application 20010047137 describes the use of a fiber optic device carrying light in the wave length rage from 1400–4100 nm as means of identifying such plaque. Casscells and Willerson in U.S. Pat. No. 5,906,636 describe a method in identifying and heating the cells with a catheter using infrared radiation. They describe that the cells are heated for a sufficient period of time (15–60 minutes) and at sufficient temperature (41–44 Degrees Centigrade) to induce programmed cell death. Speras in U.S. Pat. No. 4,799,479 also describes a similar concept of heating the plaque using thermal means to achieve the same objective.